With three young children at home, Hollywood mom Julia Roberts says her family used to waste a lot of leftover food. "I [used to] just cry and scrape plates and think, 'How can I be doing this?'"

Thanks to her eco-conscious friend Sophie Uliano, author of Gorgeously Green, Julia says she discovered a way to put her waste to good use—composting. "I do love composting," she says. "This is one of the things that Sophie has really been on me about."